This invention relates generally to the injection molding of plastic articles and deals more particularly with the molding of embossed articles such as plastic containers and the like.
A wide variety of plastic objects are formed by injection molding processes in which liquid plastic resins are injected under elevated temperature and pressure into a mold. The simplest and most economical mold arrangement is one having a cavity section held on a stationary platen and a core section carried on a movable platen which is driven toward and away from the stationary platen to open and close the mold. The mold opens and closes along a central mold axis and is commonly known as a unidirectional mold.
Although the overall simplicity and economy of this unidirectional type of mold makes it desirable for use in as many situations as possible, the shape of the article that can be formed is limited. For example, an article such as a plastic bowl or other container must have side walls which are either parallel with the mold axis or which have a draft angle relative to the axis. Otherwise, the article will engage with the cavity in a manner to remain therein when the mold is opened.
More importantly with respect to the present invention, it has not been possible in the past to effectively form embossed articles with molds of the unidirectional type. Formation of the boss requires that an engraving be cut into the mold surface to receive the material that forms the boss. If the boss is formed in an attractive shape, the upper surface of the engraving presents an "undercut" area against which the top of the boss catches during opening of the mold. Consequently, the article either fails to properly separate from the cavity as the mold opens, or the boss is sheared off or otherwise damaged by the metal cavity piece of the mold.
As a result, it has been the common practice in the past to mold embossed articles with complicated molding equipment that has moving cores or extra directional movement, and the costs have been excessive. It is thus apparent that there is a need for a molding device that is able to mold embossed articles without requiring complex movement of the mold components. The principal goal of the present invention is to meet that need.
More specifically, it is an object of the invention to provide an injection molding device of the unidirectional type which is capable of forming embossed articles such as plastic containers and the like.
Another object of the invention is to provide a molding device of the character described which readily releases the molded article without shearing or otherwise damaging the boss.
A still further object of the invention is to provide a molding device of the character described which is able to mold integral bosses that can be accurately and neatly colored by means of a standard "kiss" type printing process.
An additional object of the invention is to provide an embossed plastic article that is attractive in appearance and can be easily molded on a unidirectional injection molding machine.
Yet another object of the invention is to provide an embossed plastic article wherein each boss has an optimum size and thickness, along with an attractive appearance and an outer surface that can easily be "kiss" printed.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description of the drawings.